The present invention generally relates to naphthopyran compounds. More specifically, the present invention relates to photochromic spironaphthopyran compounds and to articles made of photochromic spironaphthopyran compounds.
Photochromism generally concerns the ability of a compound to reversibly change color under different light conditions. One particular type of photochromic phenomenon concerns the reversible change in color of a compound from an original color to a different color when the compound is exposed to a source of ultraviolet radiation, such as solar radiation or light radiated from a mercury or xenon lamp. The photochromic compound fades to the original color within a period of time after the photochromic compound is isolated from the ultraviolet radiation, such as by placing the compound in a dark room.
Various products, including optical lenses, incorporate the principal of photochromism. For example, photochromic compounds, such as naphthopyrans, are incorporated into plastic ophthalmic lenses to effect color changes in the lenses when the lenses are exposed to particular lighting conditions. Additionally, different photochromic compounds may be blended together to create a color effect that is different from respective color effects of the individual photochromic compounds. As an example, a first photochromic compound that turns orange or red when activated by light and a second photochromic compound that turns blue when activated by light may be blended together to form a photochromic mixture that produces a shade of gray when activated by light.
Several types of photochromic compounds have been reported which exhibit changes in color when exposed to ultraviolet light. One particular class of photochromic compounds includes the 3,3-disubstituted naphthopyrans. One specific group of 3,3-disubstituted naphthopyrans includes the 3H-naphtho[2,1b]pyrans. The color response of the 3H-naphtho[2,1b]pyrans to ultraviolet light extends to purple, red, orange, or yellow, depending upon the composition and structure of the particular 3H-naphtho[2,1b]pyrans. A general expression of the 3H-naphtho[2,1b]pyrans is provided in graphical formula I: ##STR2## where R.sub.3a and R.sub.3b are substituents attached to the pyran ring at the position indicated.
U.S. Pat. No. 3,567,605 to Becker describes chromenes and chromene derivatives which are photochromic at relatively low temperature. The Becker patent also describes chromenes and chromene derivatives which are photochromic at room temperature, such as diphenyl-3H-naphtho[2,1b]pyran, where R.sub.3a and R.sub.3b of formula I are each phenyl groups.
U.S. Pat. No. 4,931,221 to Heller et al. describes additional photochromic compounds, including 3H-naphtho[2,1b]pyrans represented by formula I, where R.sub.3a and R.sub.3b are cyclopropyl radicals and where any of various substituents are included on the naphtho portion of the naphthopyran rings. Heller reports that the 3H-naphtho[2,1b]pyrans which include cyclopropyl radicals exhibit a larger bathychromic shift in the visible spectrum, as compared to 3H-naphtho[2,1b]pyrans which include alkyl groups or a spirocycloallcyl group in place of the cyclopropyl radicals.
U.S. Pat. No. 5,066,818 to Gemert et al. discloses additional photochromic compounds generally meeting graphical formula I. The Gemert patent reports a range of decolorization rates associated with the 3H-naphtho[2,1b]pyrans.
U.S. Pat. No. 5,106,998 to Tanaka et al. describes compounds in which R.sub.3a and R.sub.3b of graphical formula I are alkyl groups. Tanaka reports several fade times and maximum absorption wavelengths associated with the compounds.
U.S. Pat. No. 5,238,981 to Knowles describes naphthopyran compounds of graphical formula I in which R.sub.3a and R.sub.3b are each selected from a group of organic radicals that include phenyl and naphthyl. Various potential substitutions on the naphtho portion of the naphthopyrans ring are taught, including an 8-methoxy substitution. Knowles states that number eight carbon atom substitutions, such as the 8-methoxy substitution, cause a bathychromic shift in the visible spectrum associated with activated forms of the 3H-naphtho[2,1b]pyrans and in the ultraviolet spectrum of unactivated forms of the 3H- naphtho[2,1b]pyrans.
U.S. Pat. No. 5,244,602 to Van Gemert and U.S. Pat. No. 5,274,132 to Van Gemert each describe 3H-naphtho[2,1b]pyrans of graphical formula I that include various radical substitutions at the R.sub.3a and R.sub.3b positions. Each of these Van Gemert patents also claim to achieve bathychromic shifts in the visible spectrum associated with the 3H-naphtho[2,1b]pyrans.
Another class of photochromic compounds include spironaphthopyrans, as expressed in graphical formula II: ##STR3## In formula II, R.sub.3 is attached to the pyran ring by a spiro carbon, which is a single carbon atom that is shared by two separate rings. Compounds with a single carbon atom that is common to two separate rings are called spiro compounds. Very few naphthopyrans have been disclosed in which the carbon in the number 3 position of the naphthopyran ring is a spiro carbon.
U.S. Pat. No. 4,826,977 to Heller describes a naphthopyran of formula II where R.sub.3 is the adamantyl group. Another patent, U.S. Pat. No. 4,980,089 to Heller, teaches a naphthopyran of formula II where R.sub.3 may be a bicyclic norcamphane group, a tricyclodecane group, or derivatives of either the norcamphane group or the tricyclodecane group.
Additionally, U.S. Pat. No. 5,106,998 to Tanaka et al. describes pyran compounds, such as that of graphical formula II, in which R.sub.3 is either a norbornylidene radical or a bicyclo[3,3,1]9-nonylidene radical. Tanaka reports several fade times and maximum absorption wavelengths associated with various naphthopyrans that include either the norbornylidene or the bicyclo[3,3,1]9-nonylidene radical.